In such a method, the intended relative movement of the at least two objects moving with respect to each other is simulated, where at least one of the objects is assigned an envelope surrounding the object. The path line representing the relative movement of the two objects is then covered in steps of a defined step size. To detect a possible collision of the objects, the occurrence of an overlap of the two (simulated) objects is detected while the path line is covered. For at least one of the objects, the outer contour of the corresponding envelope is used as a datum for detecting an overlap.
Such methods may be used for monitoring collisions of machine-tool parts moving relative to one another, such as a supporting table, a booth wall, a tool, a spindle head, etc., in order to be able to detect possible collisions early and prevent them with the aid of the machine control unit.
In order to be able to make the calculations necessary for simulating the movement of the individual machine parts at a sufficient rate, the objects to be monitored, e.g., those having a complicated geometric structure, are represented by an envelope that surrounds the object in question. The simulation for the collision monitoring is then conducted not on the basis of the actual geometry of the objects moving relative to each other, but rather on the basis of the geometry of the envelope, which is assigned to a specific object and is normally made of solids having a simple geometry, such as spheres, rectangular parallelepipeds, cylinders, prisms, and pyramids. Therefore, while carrying out the simulation for early detection of collisions of such objects to be monitored, which are assigned an envelope having a simple geometry, the monitoring is not focused on an overlap of the object itself and another object or its envelope, but rather on a possible overlap of the envelope assigned to the object and another object or an envelope assigned, in turn, to the other object.
In this context, the path line representing the relative movement of objects, which are moving with respect to each other and are monitored for a collision, describes the possible relative positions, which these objects may assume during the operation of a specific control program, e.g., one stored in a machine control unit. Therefore, in the case of a machine tool, the individual points of the path line correspond to a particular position of the monitored objects with respect to the machine axes of the machine tool, and namely, in view of both linear movements along the individual machine axes and rotational movements about the machine axes. Accordingly, a path line is generally understood as the set of all the relative positions, which the objects to be monitored for a collision may assume during a defined relative movement, e.g., one selected by a control program. The corresponding simulation for detecting a possible collision is conducted in the machine control unit or in a processor coupled to the machine control unit, so that the machine control unit is able to prevent a collision of the actual objects to be monitored, e.g., by stopping the relative motion or changing the relative motion.
The phrase used below that “the outer contour of the envelope assigned to the specific object is used as a datum” for detecting an overlap, i.e., mutual penetration of two objects, during the simulation means that when an overlap or mutual penetration of two (simulated) objects to be monitored is detected, the specific, actual geometries of the two objects are not used as a datum for determining overlap, but rather the envelope assigned to a specific object and the other object or the envelope assigned to a specific object and the envelope assigned to the other object are used as a datum for determining overlap, if the other object is assigned an envelope. Therefore, in the case in which the two objects to be monitored are each assigned an envelope, the mutual penetration of the two envelopes is taken into account. If only one of the two objects is assigned an envelope, the overlap of this envelope and the other object is taken into account.
A method for collision monitoring of the type described above is described, e.g., in European Published Patent Application No. 0 268 317. In this method, there is believed to be the problem that in order to reliably detect a possible collision of two objects moving with respect to each other, the path line representing the relative positions of the objects to be monitored must be covered using a step size that is as small as possible, since path-line points at which there is the danger of a collision may be skipped when the utilized step size is too large. This conflicts with the need to carry out the collision monitoring, using as little computing time as possible.